In the prior art, one type of a pressure regulation system is shown and disclosed in Japanese Pat. No. 61-268884 which is incorporated by reference. The following is a detailed explanation of structure and operation and using the same reference as noted in the specification and drawings of the above Japanese patent.
Reference is now made to FIGS. 3, 4 and 5 of the present invention which are substantially the same as FIGS. 1, 3 and 4 of the above-noted Japanese patent.
This embodiment of the prior art brake regulating system includes a pressure sensor such as deformation strain gage 21 which receives the air pressure P from the main air reservoir. The sensor converts force of the air pressure P into a corresponding output voltage signal.
As noted, a differential amplifier A1 amplifies the output voltage signal. A comparator A2 which has a hysteresis capability compares the output voltage signal V of the amplifier A1 with a pair of the standard voltage values V1 and V2. A suitable switch such as an output relay RS etc. controls the operation of the air compressor 1 in accordance with the output voltage of the comparator A2.
It will be appreciated that the above mentioned standard voltage value V1 is equivalent to the predetermined lower limit pressure value Pl of the main air reservoir pressure P. Similarly the standard voltage value V2 is equivalent to the predetermined upper limit pressure value P2. It will be understood that P2&gt;P1 so that V2&gt;V1.
During the initial stages of pressurization or charging, the compressed air is supplied to the main air resevoir which is initially at atmospheric pressure. Thus, the output voltage V of the amplifier A1 is less than the standard voltage value V1 so that the output relay RS is energized and the main supply contactor 4 is switched ON so that the air compressor 1 begins to operate.
The air pressure P supplied to the main air reservoir rises because of the operation of this air compressor 1. When air pressure becomes higher than the predetermined upper limit pressure value P2, the output voltage V of the amplifier Al also becomes higher than the standard voltage value V2 so that the output relay RS is deenergized and the main contactor 4 switches OFF. Thus the air compressor 1 shuts off.
Now when the compressed air is used or consumed by the operation of the air brake system or the like, the air pressure P in the main air reservoir obviously decreases and eventually becomes less than the predetermined lower limit pressure value Pl. Thus, the output voltage V of the amplifier A1 becomes less than the standard voltage value V1 so that the output relay RS is again energized by the turning on of the main contactor 4. Accordingly, the air compressor again begins to operate.
Thus, the air pressure P in the main air reservoir is effectively controlled to a specified pressure range, in particular between the predetermined lower limit pressure value P1 and the predetermined upper limit pressure value P2.
However, in pressure regulation systems of the prior art types for railway vehicles, the electric control circuitry normally utilize direct current circuits so that a failure occurring in a given electrical component, for example, the comparator A2 would go undetected. Further, if a failure switches the power transistor Tr 12 to an ON condition, the air compressor would continue to run in spite of the fact that the air pressure P has already reached the predetermined upper limit pressure value P2. The resulting problems may result in the burnout of the drive motor, the temperature of the discharging air increases to an intolerable level, and the ability of removing the moisture from the discharged air dramatically decreases.
The fundamental cause of this problem is that the failure of the direct current electric control circuit is not easily detected since the normal ON or OFF conditions are not discernible from an unsafe mode.